Photoelectric exposure meter



NOV. 19, 1940. GQRUCH 2,222,292

' PHOTOELECTRIC EXPOSURE METER ori inal Filed Dec. 16, '19s? 3Sheets-Sheet 1 Nov. 19, 1940. P. GGRLICH 2,222,292

PHOTOELECTRIC EXPOSURE METER Original Filed Dec. 16, 1937 3 Sheets-Sheet2 ATTORNEYS. I

NOV. 19, 1940. GURLICH 2,222,292

' PHOTOELEGTRIC EXPOSURE METER Original Filed Dec. 16, 1937 ssheets-sheet a Patented Nov. 19, 1940 UNITED? STATES 7 2,222,292PHOTOELECTRIC EXPOSURE METER Paul Gorlich, Dresden, Germany, asslgnor toZeiss Ikon Aktiengesellschai't, Dresden, Germany Original applicationDecember 16, 1937, Serial No. 180,216. Divided and this applicationFebruary 14, 1940, Serial No. 318,907.

cember 17, 1936 6 Claims.

The present invention is a division of my United States Patentapplication Serial No. 180,216, filed on the 16th day of December 1937and relates to improvements in photoelectric exposure 6 meters, inparticular in combination with photographic cameras.

In photoelectric exposure meters heretofore used a photoelectric cellwhen energized by light produces an electric current which is measuredby a measuring instrument. The size of the defiection of the pointer ofthe measuring instrument under due consideration of the selecteddiaphragm opening of the photographic lens and the sensitiveness of thephotographic emulsion indicates the required exposure time or shutterspeed for obtaining a correct exposure of the photographic emulsionunder the prevailing light conditions. Exposure meters of this wellknown type, however do not operate very accurate within the range of lowlight intensities due to poor light conditions and sometimes failcompletely which, of course, is a disadvantage.

It is the object of the invention to provide a photoelectric exposuremeter which does not have this disadvantage. This object is accomplishedby employing an entirely difierent operating principle, than heretoforeemployed in photoelectric exposure meters. In accordance with 3 thepresent invention the novel method of measuring the brightness of thescene to be photographed consists in this, that the photoelectriccurrent produced in the photoelectric cell when the latter is energizedby light, is utilized to 35 charge a condenser. The charging of thecondenser is continued for a predetermined period of time. If desiredthis'charging period may be selected in accordance with .the prevailingbrightness of the scene orobject to be photo- 40 graphed. Then thecharged condenser is discharged into a circuit in which a measuringinstrument, for instance a galvanometer, is arranged. The size of thedeflection of the pointer of this measuring instrument, under due con-45 sideration, of the duration of the charging period, indicates thebrightness of the light measured and under further consideration of thesensitiveness of the photographic emulsion and the selected diaphragmaperture of the photographic 5o lens or shutter speed respectively, isan indication of the required shutter speed or diaphragm aperturerespectively to produce a correctly exposed photographic negative.

Another object of the invention is to utilize 55 the deflection oi thepointer of the measuring In Germany Deinstrument which is actuated bythe current discharged from the condenser, directly or indirect= ly fora corresponding adjustment of a correlated camera control element, asfor instance the diaphragm adjusting member or the shutter speed cadjusting member as the case may be. 7

Other objects of the invention will be apparent or will be pointed outmore specifically in the following description with reference to theaccompanying drawings disclosing by way of ex ample a few embodiments ofthe invention.

Referring to the drawings:

Fig. 1 shows diagrammatically a photo-electric exposure meter of theinvention associated with certain exposure control elements of a.photographic camera. I

Fig. 2 shows the photographic camera in plan View, with portions brokenaway to disclose the interior mechanism.

Fig. 3 is a front elevation view of the camera and its associatedexposure meter, likewise with portions broken away.

Fig. 4 shows in an enlarged scale and partly in section the photographiclens system of the camera and illustrates the mounting of the resistancebelonging to the exposure meter.

Fig. 5 shows diagrammatically a modified ar rangement of the exposuremeter with certain control elements of a photographic camera.

Fig. 6. shows diagrammatically a combination of the arrangementsillustrated in the'Figs. 1 and 5.

Fig. '7 illustrates the arrangement of the resistance of the exposuremeter in combination with the shutter speed adjusting element of thecamera in accordance with the modification of Fig. 5.

Figs. 8 and 9 illustrate diagrammatically the operation of theindicators of the measuring instrument in different positions. 40

Fig. 10 is a plan view of the indicating means of the measuringinstrument, and

Fig. 11 is an elevation view of the indicating means, partly in verticalsection.

In the diagrammatic illustration of Fig. 1, the photoelectric cell l isnormally. protected against the light by a cover 2 adapted to be movedmanually away from the front of the cell. The cover 2 may be pivotallyattached to the mounting or casing of the photoelectric cell I by ahinge as indicated at 2' in Fig. 3.

For determining the correct exposure time the photoelectric cell i hasto beexposed to the light reflected from the scene or object to besistance 1 and the measuring instrument 6 is opened. A condenser 6arranged in circuit with the photoelectric cell i is now charged withthe photo current generated in the cell. This charging operation iscontinued until the cover 2 is automatically closed by the previouslytensioned spring motor I which is provided with suitable retarding means(not shown) to eifect a closi of the cover 2 after a predeterminedinterval of time. At the instant the cover 2 is closed the switch 6 isclosed again and the condenser 6 is discharged over the galvanometer 6whose pointer I2 is deflected in accordance with the intensity of theelectric current passing through the in- U strument 6.

Prior to operating the exposure meter in the described manner it isnecessary to adjust the variable resistance I with respect to the filmspeed and the size of the diaphragm aperture of the camera lens. Asindicated diagrammatically in Fig. 1 any change in the adjustment of thediaphragm aperture is compensated for by a corresponding adjustment ofthe slidable contact member 6 of the resistance 'I.- The film '30 speedis taken into consideration by a suitable The Figs. 2. 3 and 4illustrate a practical embodiment of a camera and exposure meteroperating in accordance with the diagrammatic showing of Fig. 1. TheFigs. 2 and 3 disclose that the shutter speed adjusting member I0 ismounted on the top wall of the camera casing and is operativelyconnected by a train of gears II, l4, I6 and I6 with a radial arm ilfixedly secured to the last gear I6 of said train of gears. The outerend of this arm I6 is bent twice to extend into the casing 6' of themeasuring instrument I mounted together with the photoelectric cell 2 onthe outside of the camera top wall. The outermost end of this arm I6 isprovided with the mark H and comes to lie in a plane just'below theplane in which the pointer i2 of the measuring instrument 6 is deflected(Fig. 3). 5 The camera lens system 30 mounted on the front wall of thecamera casing is provided with a knurled ring I! (Figs. 2 and 4) foradjusting the size of the diaphragm aperture indicated at 21 (Fig. 4).The lens system 30 is focused by ro- 5 tating the ring 32 provided withan actuating knob l8.

Fig. 4 illustrates all mechanical details of the adjusting devicesindicated diagrammatically in Fig. 1 with I, 8 and 9. It will be notedthat the resistance 1 is mounted on a radial shoulder of the lens barrelIS. The contact member 6 which slidably engages the resistance 1 isconnected by means of an intermediate ring 20 with the diaphragmadjusting ring IT. The rings I1 and 20 are rotatably adjustablyconnected with each other by a tight fitting thread 22 of very lowpitch, but usually rotate as a unit. The intermediate ring 20 isprovided with a window It through which a scale indicating film speedsand arranged on the diaphragm ring I! can be ob- I served. Theadjustment for film speed is effected by rotating the rings l1 and 26relatively to each other until the desired film speed number appears inthe window 2|. The insulated contact member 23 which is connected withone ter- 10 minal of the galvanometer 6 slidably engages an insulatedconductor ring 34 in the inner end of the lens barrel l9 and aninsulated conductor 35 leads from the ring 24 to one end of theresistance I. The other current conductor of the circuit is formed inknown manner by the metallic camera casing and metallic portionsof thelens mounting.

Fig. 5 illustrates diagrammatically a modification of the exposure meterarrangement of 20 the invention. In this modification the running offperiod of the spring motor 3 and during which the cover 2 remains openis not constant, but is varied in accordance with the adjustment of thediaphragm apertures by means of the ring 25 ll. Each selected diaphragmaperture 4| corresponds to a predetermined period of time during whichthe cover 2 remains open. In other respects, however, the modificationof Fig. 5 may be the same as the first described embodiment.

'The shutter speed adjustment may be accomplished also by rotating theshutter speed adjusting member I0 until the mark II on the lever l6"coincides with the pointer i2 as deflected by the current dischargedfrom the condenser 6. ,5

It is, however, also possible to combine the variable resistance of theexposure meter with. the shutter speed adjusting member ID instead ofwith the lens system. Such an arrangement is shown in Fig. 7 and morediagrammatically in 0 Fig. 5. The slidable contact member 26 of theresistance 24 is fixedly attached to the shutter speed adjusting memberl0 and when the latter is rotated the resistance 24 is varied. Themember I0 is rotatably adjusted until the pointer l2 of the galvanometerpoints .to a predetermined mark or is returned to its zero position, asthe particular case may be. In Fig. 7 the shutter speed adjusting memberill carries in its center the customary shutter release button 36 whichwhen depressed actuates the slidably mounted shutter release rod 31. Thebutton 36 is provided with a threaded conical bore 38 for selectivelyattaching thereto a well known cable release for the shutter, ifdesired.

Referring now to Fig. 6, it will be noted that the same illustrateddiagrammatically a combination of the resistance adjustments I and 9correlated with the diaphragm adjustment and film speed adjustment ofFigs. 1 to 4 and the shut- I ter speed adjustment of Figs. 5 and 6according to which the resistance 24 coupled with the shutter speedadjusting member III is varied by the member l0 until the pointer l2 ofthe measuring instrument 6 comes to rest opposite a fixed mark or isreturned to its zero position. In this last embodiment there will appeartwo variable resistances I and 24 in the circuit of the exposure meter,but the train of gears I) to I 6 and the radial indicating arm l6 areeliminated. 70

The measuringinstrument 6 is preferably a ballistic galvanometer, sothat the pointer may remain as long in its deflected position asnecessary for an exact reading of the scale. Referring now to the Figs.8 to 11 with respect to the 15 operation of the measuring instrument,the mark II is set in the position indicated by the pointer I2. I alsoprovide another performance of this construction by the use of anauxiliary pointer l2, which is taken along by the pointer II to itsmomentary maximaldeilection. Then the pointer l2 returns to its zeroposition, while the auxiliary pointer I2 remains in the above mentionedmaximal position, thus making possible to read the position of thepointer even after a longer time; The mark H is then brought tocoincidance with the auxiliary pointer l2. The latter is provided with ashort pin I2 extending through the slot |2. By moving this pin H to theleft the latter may .be brought in its zero position or in any otherposition, hereby making it possible to set the exposure time, it a markit is not provided.

What I claim is:-

1. The combination with a photographic camera including a casing, aphotographic lens system having a variable diaphragm and a diaphragmadjusting member, of a photoelectric exposure meter, comprising aphotoelectric cell mounted on said casing and provided with a covernormally protecting the cell against light, a condenser conductivelyconnected with said cell and adapted to be charged bythe photo cellcurrent produced in said cell, a measuring instrument, conductor meansincluding a switch and a variable resistance in a circuit with saidcondenser, and a spring motor connected with said cover and tensioned bythe same when the cover is moved to open position, said spring motorclosing saidcover automatically after a predetermined period of time,said switch being operatively connected with said cover so as to beopened when said cover is opened and being closed again at the instantthe spring motor has closed said cover, said resistance being mounted onsaid photographic lens system and being varied-by said diaphragmadjusting member whenever the aperture of the diaphragm is varied.

2. The combination with a photographic cam era including a casing, ashutter speed adjusting member on said casing, a photographic lenssystem having a variable diaphragm and a dia-- phragm adjusting member,of a photoelectric exposure meter comprising a photoelectric cellmounted on said casing and provided with a cover normally protecting thecell against light, a cone denser conductively connected with said celland adapted to be charged by the photo cell current produced in saidcell, a measuring instrument, conductor means including a switch and avariable resistance in a circuit with said condenser, a spring motorconnected with said cover and tensioned by the same when the cover ismoved to open position, said spring motor closing said coverautomatically after a predetermined period of time, said switch beingoperatively connected with said cover so as to be opened when said coveris opened and being closed again at the instant the spring motor hasclosed said cover, said resistance being mounted on said photographiclens system and being varied by said diaphragm adjusting member wheneverthe aperture of the diaphragm is varied, and means operatively connectedwith said shutter speed adjusting member and adjusted simultaneouslywith the latter for setting the speed of the shutter ir. accordance withthe indication of said measuring instru ment.

3. The combination with a photographic camera including a casing, ashutter speed adjusting member on said casing, a photographic lenssystem having a variable diaphragm and 8. diaphragm adjusting member, ofa photoelectric exposure meter comprising a photoelectric cell mountedon said casing and provided with a cover normally protecting the cellagainst light, a condenser conductively connected with said cell andadapted to be charged by the photo cell current produced in said cell, ameasuring instrument, conductor means including a switch and a variableresistance in a circuit with said condenser, a spring motor connectedwith said cover and tensioned by the same when the cover is moved toopen position, said spring motor closing said cover automatically aftera predetermined period of time, said switch being operatively connectedwith said cover so as to be opened when said cover is opened and beingclosed again at the instant the spring motor has closecl'said cover,said resistance being mounted on said photographic lens system andbeing-varled by said diaphragm adjusting member whenever the aperture ofthe diaphragm is varied, and another variable resistance in the circuitin which said measuring instrument is arranged, said last namedresistance being varied by said shutter speed adjusting member untilsaid measuring instrument has been adjustedto a predetermined valuewhich indicates that the shutter speed has been correctly adjusted forthe prevailing light conditions and diaphragm aperture. 4. Thecombination with a photographic camera including a casing, aphotographic lens system having a variable diaphragm and a diaphragmadjusting member, of a photoelectric exposure meter comprising aphotoelectric cell mounted on said casing and provided with a covernormally protecting the cell against light, a condenser conductivelyconnected with said cell current produced in said cell, a measuringinstrument, conductor means including a switch and a variable resistancein a circuit with said condenser, and a spring motor connected withsaidcover and tensioned by the same when the cover is moved to openposition, said spring motor closing said cover automatically after apredetermined period of time, said switch being operatively connectedwith said cover so as to be opened when said cover is opened and beingclosed again at the instant the spring motor has closed said cover, saidresistance being mounted on said photographic lens system and being eraincluding a casing, a shutter speed adjusting,

member on said casing, a photographic lens system having a variablediaphragm and a diaphragm adjusting member, of a photoelectric exposuremeter comprising a photoelectric cell mounted on said casing andprovided with a cover normally protecting the cell against light,

a condenser conductively connected with said,-

cover and tensioned by the same when the cover is moved to openposition, said spring motor closing said cover automatically after apredetermined period of time, said switch being operatively connectedwithsaid cover so as to be opened when said cover is opened and beingclosed again at the instant the spring motor has closed said cover, saidresistance being mounted on said photographic lens system and beingvaried by said diaphragm adjustinfl member whenever the aperture of thediaphragm is varied, means associated with said diaphragm adjustingmember for adjusting said resistance for diiferent film speeds, andmeansnperatively connected with said shutter speed adjusting member andadjusted simultaneously with the latter for setting the speed of theshutter in accordance with the indication of said measuring instrument.

6. The combination with a photographic camera including a casing, ashutter speed adjusting member on said casing, a photographic lenssystem having a variable diaphragm and a diaphragm adjusting member,'ota photoelectric exposure meter comprising a photoelectric cell, mountedon said casing and provided with a. cover normally protecting the cellagainst light, a condenser conductively connected with said cell andadapted to be charged by the photo cell current produced in said cell, ameasuring instrument, conductor means including a switch and a variableresistance in a circuit with said condenser, a spring motor connectedwith said cover and tensioned by the same when the cover is moved toopen position, said spring motor closing said cover automatically aftera predetermined period of time, said switch being opergatively connectedwith said cover so as to be opened when said cover is opened and beingclosed again at the instant the spring. motor has closed said cover,said resistance being mounted on said photographic lens system and beingvaried by said diaphragm adjusting member whenever the aperture 0! thediaphragm is varied, means associated with said diaphragm adjustingmember for adjusting said resistance for different flim speeds, andanother variable resistance in the circuit in which said measuringinstrument is arranged, said last named resistance being varied by saidshutter speed adjusting member until said measuring instrument has beenadjusted to a predetermined value which indicates that the shutter speedhas been correctly adjusted for the prevailing light conditions anddiaphragm aperture.

PAUL common.

